1. Field of Invention
This invention relates generally to electro-optic (EO) modulators, and more particularly to lithium niobate Mach-Zehnder interferometer (MZI)-type modulators.
2. Description of the Prior Art
EO modulators are used to adapt an optical channel to carry information such as telephone calls and digital electronic data, for transmission over lightwave networks. Lithium niobate MZI-type modulators are known and described, for example, in E. L. Wooten, K. Kissa, et al., xe2x80x9cA review of lithium niobate modulators for fiber-optic communications systemsxe2x80x9d IEEE Journal of Selected Topics in Quantum Electronics 6 (1) January/February 2000, pp. 69-82. Such modulators are typically adapted, for electrical signal input connection, with an RF waveguide electrode arrangement with xe2x80x9chornsxe2x80x9d, as shown for example in M. M. Howerton et al., xe2x80x9cFully packaged, broad-band LiNbO3 modulator with low drive voltagexe2x80x9d IEEE Photonics Letters 12 (7) July 2000, pp. 792-794. The electrical signal connection is further constrained to a characteristic impedance of approximately 50 xcexa9 for interfacing with coventional RF drive components. The combination of a horn electrode arrangement, RF drive (electrical signal input) connection by ribbon or wire bonds, and 50 xcexa9 impedance, constrain existing modulators to relatively large sizes and high drive power requirements, which are obstacles to their integration in arrays. Improved EO modulators with smaller area and lower drive power requirements are therefore desirable, for next generation lightwave systems employing array components.
In accordance with an embodiment of the invention, a Mach-Zehnder modulator is provided which comprises a waveguide formed to enable formation of a tightly confined, xe2x80x9csqueezedxe2x80x9d optical mode with an elliptical mode profile, close to the optical chip surface, in order to achieve maximum overlap of the optical mode with the highest intensity regions of an electric field generated by RF electrodes.
In accordance with yet another embodiment of the invention, a Mach-Zehnder modulator is provided which comprises laterally recessed adhesion layer disposed between an electrode and the substrate, the adhesion layer recessed by a sufficient distance to minimize the dissipative (lossy) effect it would have on the propagation of RF energy along the proximal edges the electrode.
In accordance with a further embodiment of the invention, an electro-optic modulator is provided, configured to operate under dual drive conditions.
In accordance with yet a further embodiment of the invention, an integrated electro-optic modulator array is provided.